1. Field of the Invention
The present invention generally relates to a vehicle drive force control apparatus for a vehicle having a wheel or set of wheels driven by a main drive source and an electric generator also driven by the main drive source. Preferably, an electric motor is driven with electric power generated by a generator that is driven by the main drive source. The present invention especially useful in an all wheel drive vehicle in which a pair of main drive wheels are driven by the main drive source, such as an internal combustion engine, and a pair of subordinate drive wheels are driven by the electric motor. Thus, the invention is particularly well-suited for a so-called battery-less four-wheel drive vehicle in which the engine drives the generator and the electric power from the generator is supplied to the electric motor.
2. Background Information
One example of a drive force control apparatus is disclosed in Japanese Laid-Open Patent Publication 2000-318473. The drive force control apparatus of this publication discloses a vehicle in which the front or main drive wheels are driven by an internal combustion engine, and the rear or subordinate drive wheels are driven by an electric motor. The electric motor is driven by electric power generated by an electric generator that is driven by the engine. When the drive force control apparatus disclosed in this publication is used, it is not necessarily mandatory to have a battery that supplies electric power to the electric motor. Furthermore, the device presented in this publication is configured to assist with acceleration from a stopped condition by driving the rear wheels with the electric motor only when the vehicle is starting into motion from a stop.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved vehicle drive force control apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.